Diesel engines are a type of compression ignition engine. Compression ignition engines ignite fuel by compressing a quantity of air in a combustion chamber during a compression stroke. In particular, a piston compresses the air within the combustion chamber and the heat generated by the compression of the air increases the temperature within the combustion chamber. Once the temperature in the combustion chamber surpasses a threshold level, fuel injected into the combustion chamber ignites. Ignition and subsequent combustion of the fuel generates high pressure gases which act on the piston which causes a crankshaft of the diesel engine to rotate.
However, the temperature of the air in the combustion chamber at the end of the compression stroke also depends on the temperature of the air entering the combustion chamber prior to the compression stroke. During cold weather, the temperature of the air entering the combustion chamber may be low enough that the temperature rise in the combustion chamber during the compression stroke is not sufficient to raise the temperature of the combustion chamber above the threshold temperature. Under such conditions, the engine will not start or run. Increasing the temperature of the air advanced into the combustion chamber prior to the compression stroke will increase the temperature in the combustion chamber during the compression stroke and cause the injected fuel to ignite in the combustion chamber.
In addition, even under conditions where the fuel does ignite, the temperature in the combustion chamber may not be high enough to completely combust all of the fuel in the combustion chamber. The unburned fuel, also known as unburned hydrocarbons, is exhausted into the atmosphere. These unburned hydrocarbons are a visible form of pollution known as white smoke. Current emission standards limit the amount of unburned hydrocarbons that can be emitted during the operation of the diesel engine. In addition, future emission standards may limit the amount of unburned hydrocarbons that can be emitted into the atmosphere during cold start-up conditions. Increasing the temperature of the air in the combustion chamber prior to the compression stroke will also decrease the amount unburned hydrocarbons advanced into the atmosphere during cold start-up conditions.
Diesel engines heretofore designed have used several devices to increase the temperature of the air advanced into the combustion chamber prior to the compression stroke. These devices include air pre-heaters which heat the air in the intake manifold prior to the air being advanced to the combustion chamber. These pre-heaters add cost and complexity to the design of the diesel engine as the pre-heater requires a fuel burner or electrical heating element to heat the air in the intake manifold. Another solution is to use a coolant heater to heat the engine coolant that surrounds the cylinders. Heating the cylinder walls also increases the temperature of the air in the cylinder. The added cost and complexity of a fuel burner or electrical heating element is required to heat the coolant in the diesel engine. As yet another solution, fuels with lower ignition temperatures, such as ether can be advanced to the combustion chamber to initiate ignition of the diesel fuel. Again, additional costly and complex equipment is required to store a separate fuel that is used only during cold start-up conditions.
What is needed therefore is an improved method and apparatus which increases the temperature in the combustion chamber of a diesel engine during cold start-up conditions. In addition, it is desirable that the method and apparatus does not require additional costly or complex equipment to be added to the diesel engine.